OBJECTIVES To investigate whether phase angle (PhA) measured by bioelectrical impedance analysis (BIA) and frailty are associated with the outcomes of critical illnesses.

DESIGN A single-center prospective cohort study.

SETTING Medical intensive care unit (ICU) in Seoul National University Hospital, Seoul, Republic of Korea.

PARTICIPANTS 97 patients who were admitted to the medical ICU.

MEASUREMENTS On admission, PhA was measured by BIA, and frailty was assessed by the Korean Modified Barthel Index (KMBI) scoring system. Patients were classified according to PhA and KMBI scores, and their impact on the outcomes of critical illnesses was evaluated.

RESULTS The patients' mean age was 62.4 ± 16.4 years, and 56 of the patients (57.7%) were men. Having a high PhA above 3.5 at the time of ICU admission was associated with lower in-hospital mortality (adjusted OR 0.42, p = .042), and a shorter duration of ICU stay (5.6 days vs. 9.8 days, p = .016) compared to those with a low PhA. Other indices measured by BIA were not significantly associated with outcomes of critical illnesses. Frailty (KMBI > 60) was associated with more mechanical ventilation days (2.3 days vs. 7.1 days; p = .018).

CONCLUSION Both PhA and frailty are important prognostic factors predicting the outcomes of critical illnesses. Low PhA scores were associated with increased mortality and a longer duration of ICU stay, and frailty was associated with more mechanical ventilation days.